There are many applications wherein it is desirable to separate solids from liquid/solid slurries, either for the purposes of reclaiming or recycling the separated components of the slurry, or for enabling more efficient handling or processing of the separated or "processed" components. One application, for example, is the separation of sand or particulate or granular materials from slurries of such materials. In such application, the primary purpose would be to reclaim the particulate sand from the slurry. Another application which is specifically addressed by the preferred embodiment of this specification is the removal of solids from animal waste slurries. Such processing of animal waste slurries not only allows for more efficient disposal of the removed solids, but also enables the remaining liquid and/or slurry material to be effectively and efficiently pumped for further direct use or processing.
Animal waste or manure is typically collected in a barn or other animal housing structure through slotted floors or in collection troughs or the like, and is moved either manually or by automated means toward collection reservoirs or pits. The consistency of such waste slurries includes organic solid wastes, fibrous materials such as bedding hay or the like, sand and liquids. It has been found that an optimum consistency of such waste slurries for pumping by impeller-type pumps are those that contain on the order of 5-6% solids. Such compositions can be more easily pumped and processed, with smaller, lower powered pumps and agitators. Alternatively, higher powered pumps can perform with greater efficiency. Further, it is desirable to remove as much abrasive material such as sand, and fibrous material such as hay and bedding material from the slurry prior to pumping.
In colder climates wherein the animal waste may be forced by piston pumps through underground conduits to remote storage reservoirs (as for example described in my prior U.S. Pat. Nos. 3,876,341 and 4,439,115) it is also desirable to preprocess such animal waste slurries prior to pumping by the piston pumps in order to facilitate operation of the pumps and to remove most of the fibrous material from the slurry which is a significant cause of blockage within the underground transport conduits, and which can cause the various movable valve portions of such pumping systems to hang-up or bind. Such blockages or valve malfunctions can result in costly, potentially dangerous system cleaning and/or repair operations and pressurized gas buildup in the underground lines.
One technique for simply reducing the percentage of solids in a slurry (as for example, to get down to the desired 5-6% solids figure) is to simply add water or other liquid to the slurry until the desired consistency is attained. This technique is generally unsatisfactory since it greatly increases the volume of materials requiring pumping and disposal or storage. Further, such technique does not address the problem of removal of undesirable solids such as sand or fibrous material from the slurry prior to pumping.
The best solution, therefore, is to physically remove unwanted solids from the slurry prior to pumping and/or further processing of the slurry. To date, however, known techniques for removing solids from slurries such as animal waste slurries have not been particularly efficient or flexible in use. The most commonly used such system is configured in the form of a screen-like surface engaged by a plurality of conveyor-like moving metal paddles that push the waste material along and over the screen or grid surface such as illustrated in U.S. Pat. Nos. 4,666,602 or 5,268,100. The theory of operation of such systems is that the liquid portion of the slurry will pass through the porous screen surface for collection below the screen, and the solids will be pushed along over the screen surface and collected at one end. Such apparatus is highly susceptible to wear and requires significant maintenance due to constant sliding engagement between the metal screen and conveyor blade members. Further, a portion of the solids tend to be "squeezed" through the screen by the sliding blades and back into the collected liquid portion where they have a tendency to resolidify. In addition, fibrous materials such as hay and straw have a tendency to stick or catch in the screen, causing potential binding and/or inefficiency of operation.
Others have used rotary drum-shaped screen filters for filtering solids from slurry materials. An example of such apparatus is illustrated in U.S. Pat. No. 4,426,289. The slurry is introduced to the interior of a screen-type drum filter and is pushed along the interior surface of the drum as it rotates while the liquids pass through the mesh surface of the drum. Other rotary drum filter structures, such as those used in roll press applications, pass slurry over the external surface of a rotary drum screen filter through which the liquid passes. A press roll can be used in association with the filter drum to squeeze the slurry material between the press roll and the underlying drum filter to further extract liquids from the solids. As with the conveyor-type structures, these known rotary separators use simple filtration for performing the solids separation from the slurry, but also generally require frictional engagement between the filtration screen mechanism and another structure to advance the filtered solids. Also, such filtration structures do not generally reuse the filtered liquid to assist in washing of slurry material that is yet to be separated.
A system that lifts solids from a slurry in a flow-through sewage system is shown in U.S. Pat. No. 1,920,158. Such system uses a bucket conveyor to scrape solids from a filtering screen and to lift solids from a slurry to a discharge chute. The system suffers from its use of moving conveyor parts that are inherently susceptible to failure in the raw sewage environment in which they work, and from wearing frictional engagement of the buckets with the filtration screen and collection pit from which the buckets scrape their solids.
The present invention addresses the needs and shortcomings of prior art separators and separation techniques. The present invention provides a very simple, yet effective technique for separating solids from slurries in a highly efficient and reliable manner and with apparatus that takes a minimum of physical space, and is highly reliable, uses a minimum of movable parts and which is readily adaptable for use with a large variety of slurry materials and in a number of different applications.